Electrophilic substitution with rearrangement. Part VII. Reaction paths in the bromination of cholest-4-en-3-one

Abstract

The bromination of cholest-4-en-3-one can occur by a number of reaction paths. Conditions under which reaction can be established as occurring in part by electrophilic attack on (a) cholesta-3,5-dien-3-ol, (b) cholesta-2,4-dien-3-ol or its anion, and (c) cholest-4-en-3-one have been identified; among the products can be included 2α-, 4-, 6β-, and 6α-bromocholest-4-en-3-one; 2α,6β-, 2α,6β, and 4,6β-dibromocholest-4-en-3-one; and 2α,4,6β-tribromocholest-4-en-3-one. Unstable adducts invovling the 4,5-double bond are implicated in a number of cases. Preliminary studies of the bromination of choest-5-en-3-one also indicate complexities, some of which involve addition to the 5,6-double bond. The rates and mechanism of reversible isomerisation of 6β- to 6α-bromocholest-4-en-3-one, and of 2α,6β- to 2α,6α-dibromocholest-4-en-3-one, have been partly elucidated.